1. Field of the Invention
This invention relates to photography and more particularly to color diffusion transfer photography employing sulfonamido compounds which are preferably alkali-cleavable upon oxidation to release a diffusible photographically useful group.
2. Description Relative to the Prior Art
Various formats for color diffusion transfer assemblages are described in the prior art, such as U.S. Pat. Nos. 2,543,181; 2,983,606; 3,362,819; 3,362,821; 3,592,645; 3,785,815; 3,415,644; 3,415,645; 3,415,646; 3,647,437; 3,685,707 and 3,756,815, and Canadian Pat. Nos. 928,559 and 674,082. In these formats, the image-receiving layer containing the photographic image for viewing can be separated from the photographic layers after processing, or, in some embodiments, it can remain permanently attached and integral with the image-generating and ancillary layers present in the structure when a transparent support is employed on the viewing side of the assemblage. The image is formed by color-providing substances released from the image-generating units, diffusing through the layers of the structure to the dye image-receiving layer. After exposure of the assemblage, an alkaline processing composition permeates the various layers to initiate development of the exposed photosensitive silver halide emulsion layers. The emulsion layers are developed in proportion to the extent of the respective exposures, and the image dyes which are formed or released in the respective image-generating layers begin to diffuse throughout the structure. At least a portion of the imagewise distribution of color-providing substances can diffuse to a dye image-receiving layer to form an image of the original subject in that layer. A retained image is also obtained consisting of the dye-providing compound that remains in the unexposed areas.
A process of this type is described in French Pat. No. 2,154,443 wherein a photographic film unit is used which comprises at least one dye image-providing element consisting of at least one silver halide light-sensitive element having associated therewith a nondiffusible compound capable of releasing a dye, hereinafter referred to as a redox releaser. The redox releaser comprises a sulfonamidophenol or sulfonamidoaniline moiety and a dye or dye precursor moiety which can be released during photographic processing by an oxidation-reduction reaction. After imagewise exposure, the photographic film unit is processed with an alkaline solution in the presence of a silver halide developing agent. In each dye image-providing element, a negative silver image is developed and an imagewise distribution of oxidized developing agent is formed which is cross-oxidized with the nondiffusible dye image-providing redox releaser. As a result, an alkali-cleavable compound is formed which will release a diffusible dye or dye precursor as a function of the exposure received by each of the silver halide light-sensitive layers. The diffusible dye images formed in each image-providing element are then removed, either by allowing them to migrate by diffusion into the processing bath, or by transferring them onto a mordant-containing sheet. A retained image is also obtained in the photographic film unit. If the silver halide light-sensitive emulsions of the film unit are negative emulsions, i.e., emulsions that give negative images upon exposure to a positive original, the retained image is a redox releaser color image positive with respect to the the original. In this case, the redox releaser is a color compound or a compound which becomes colored upon processing. The photographic film unit which carries the positive color image comprises also a negative silver image and a positive imagewise distribution of unexposed and undeveloped silver halides. If it is desirable to keep the positive color image only, it is necessary to remove by known processes the residual silver halides and the developed silver image, for example by bleaching followed by fixing, such as described in U.S. Pat. No. 3,923,510.
In many instances, the dye images obtained as described above do not exhibit satisfactory sensitometric characteristics. In particular, minimum densities are often undesirably high. In the prior art processes in which the retained image is kept, the image must be bleached to obtain a satisfactory minimum density.
These prior art processes, such as described in the aforementioned French Pat. No. 2,154,443 have, in particular, the disadvantage of providing minimum densities which contribute to the formation of unwanted stain. Without the following theory limiting the scope of the present invention, it may be assumed that the stain results from the following reaction mechanisms:
1. As previously mentioned, the redox releaser is oxidized upon processing and releases a diffusible dye (or dye precursor) but it also releases a nondiffusible quinone, this reaction being represented as follows: ##STR2##
2. The quinone formed is subjected to a hydroxylation reaction, generally in the 3-position, represented by the following mechanism: ##STR3##
3. This hydroxylation product is then oxidized into a hydroxyquinone, which reaction is represented as follows: ##STR4##
This 3-hydroxyquinone which is insoluble in the processing solution and remains in the processed photographic film unit is yellow in color and contributes substantially to the stain in the retained color images. The use of redox releasers which are substituted, for example, in the 3-position, would prevent the formation of the 3-hydroxyquinones responsible for unwanted stain according to the above reaction mechanisms. It is thus seen that substituted sulfonamido compounds are desirable for use as redox releasers in photosensitive elements, film units, and processes for retaining a color photographic image with reduced stain.